The pancreatic islets of Langerhans are largely comprised of beta- and alpha-cells that secrete specific hormones in response to plasma glucose levels. Beta-cell insulin reduces blood glucose levels by promoting glucose uptake into tissue, while glucagon from alpha-cells induces release of glucose into circulation from stores. The exquisite control by these opposing islet hormones allows for physiological maintenance of blood glucose levels. However, glucose homeostasis defects result from an autoimmune beta cell attack in type 1 diabetes or beta cell dysfunction during type 2 diabetes, two major public health threats. Poorly managed diabetes results in chronic side effects associated with improper blood glucose control (e.g. heart disease, neuropathies, retinopathy and kidney failure). With the advent of islet transplantation protocols, scientists are on the cusp of freeing patients from insulin injections and/or pharmacological intervention. However, patient demand for islets far outnumbers existing donor supplies. Sustainable and innovative treatments must be developed that improve quality of life for patients.

Future diabetes care will focus on novel cell-based therapies involving in vitro generation of functional and renewable beta-cells for transplantation, as well as strategies to promote regeneration of a patient’s own beta-cells. To be successful, we must exploit current and future knowledge of the complex developmental processes and genetic programs that produce functional pancreatic beta-cells. Specifically, the Hunter lab is focused on the LIM-Homeodomain class transcription factor, Islet-1, previously shown to be required for beta-cell development, maturation and function. We have also recently demonstrated that a transcriptional co-regulator, Ldb1, which interacts with Islet-1 and other related LIM transcription factors, is required for Islet-1 mediated gene regulation and islet cell development. Strikingly, we also observed Ldb1 beta-cell target genes that are independent of Islet-1, suggesting that additional LIM family members interact with Ldb1 and are active in the developing beta-cell. Our future studies will seek to address the lack of knowledge in the islet field regarding transcriptional co-regulators and their roles with transcription factors. We use biochemical assays including protein purification, Electrophoretic Mobility Shift Assay (EMSA), ImmunoPrecipitation (IP), and Chromatin ImmunoPrecipitation (ChIP) to characterize and identify transcription factors. We also study the effects after siRNA-mediated knockdown of transcriptional regulators in β-cell lines (βTC-3, Min6, and INS-1). In addition, we use mouse models to study the in vivo roles of these factors via Cre/Lox technology. Comparative genome-wide gene expression studies (i.e. microarray and RNA-seq), genome-wide target DNA-binding (i.e. ChIP-Seq), and protein interaction approaches will also define Ldb1 target genes and interacting factors, as compared with Islet-1. Our overall hypothesis is that Ldb1 organizes transcriptional complexes comprised of LIM transcription factors (including Islet-1) and other interacting coregulators to control early pancreas formation, endocrine cell maturation and adult islet function. These studies may reveal additional factors and target genes with roles in pancreatic islet formation and function, which could be exploited toward generating therapeutic beta cells.